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New synthetic and characterization strategies for polyolefins

Luruli, Nyambeni (2007-03)

Thesis (PhD)--University of Stellenbosch, 2006.

Thesis

ENGLISH ABSTRACT: Metalloxycarbene complexes [(CO)5M1=O(R)M2(Cl)L2] (M1 = Cr , W; M2 = Zr, Hf; L =
Cp, Cp*) were synthesized from the reaction between anionic Fischer-type carbene
complex salts [(CO)5M1=C(O)R][NEt4] and metallocene chlorides. The molecular and
crystal structures of [(CO)5W=C(Me)OZr(Cp)2Cl], [(CO)5Cr=C(Me)OZr(Cp)2Cl] and
[(CO)5W=C(Ph)OHf(Cl)Cp2] determined by X-ray methods, show a short Ccarbene-O and
relatively long O-Zr and O-Hf separations. Metalloxycarbene complexes in the presence
of MAO are active catalysts for homo- and copolymerization of -olefins and produce
polymers with heterogeneous properties. 1-Pentene oligomers, homopolymers of ethylene
and ethylene/1-pentene copolymers were successfully synthesized using
metalloxycarbenes/MAO and the results obtained were critically compared with those
synthesized with metallocene/MAO catalysts. The GC and GPC show that 1-pentene
oligomers produced with both metalloxycarbenes and metallocenes catalysts range from
simple dimers to more complicated high molecular weight (2 600 g/mol) products. The
properties of polyethylene and ethylene/1-pentene copolymers were evaluated by, among
others, GPC, SEC-FTIR, preparative molecular weight fractionation and HPer DSC.
Generally the polymers obtained using metalloxycarbene/MAO catalysts have broad and
bimodal molecular weight distributions. The copolymers have higher concentration of 1-
pentene in the lower molecular weight fraction than those produced with metallocene/MAO as shown by SEC-FTIR. Consequently, HPer DSC shows a decrease
of melting and crystallization temperature towards the low molecular weight fractions.